1Universitätsklinikum Leipzig Klinik und Poliklinik für Kardiologie Leipzig, Deutschland; 2Innovation Center Computer Assisted Surgery Leipzig, Deutschland; 3Gesellschaft für Angewandte Medizinische Physik und Technik Merseburg, Deutschland
Introduction: Survival after out-of-hospital cardiac arrest (OHCA) is still dismal. Feedback devices to ensure high-quality chest compression might improve outcomes. We set out to develop a novel feedback device using carotid ultrasound. Our aim is a device which can be deployed rapidly and reliably by non-ultrasound-trained medical personnel, and which gives clear feedback concerning the quality of chest compression.
Methods and Results: We used a specifically developed and compactly build ultrasound probe employing three ultrasonic elements in order to account for the unknown angle of doppler ultrasound insonation (patent pending, Fig. 1 A, denoted by asterisk). The probe uses pulsed-wave (pw) doppler ultrasound. To place the probe reliably, we constructed a mounting using a Stifneck extrication collar (Laerdal Medical, Copenhagen, Denmark, Fig 1 A and B). The probe can be slid along the mounting on a rail, covering different positions (Fig 1 A, denoted by arrow).
We evaluated the power score defined as the transformation of the entire determined blood flow curve into the image/frequency range by the discrete Fourier transformation, in which the powers of the periodic parts of the flow curve are determined and plotted as a function of frequency as a parameter of signal quality at 5 different positions denoted as millimeter (mm) positions along the rail in the mediolateral direction in each subject and at 7 different depths between 3.75 – 27.75 (mm) of the pw doppler window. We tested the probe and the collar on n=25 volunteers. Data are presented median (interquartile range p0,25 – p0,75).
Anthropometric baseline characteristics are height 185 (169 – 189) cm, weight 73 (63 – 79) kg, BMI 22.25 (21.45 – 23.13) kg/m², neck circumference 37 (34.0 – 38.5) cm, neck length 19.5 (17.0 – 21.5) cm. The evaluation yielded interpretable doppler spectra between positions 35 mm and 95 mm in the mediolateral direction in most of the subjects (Pos. 55 mm: 86.4% of subjects, 65 mm: 63.6 % of subjects, 75 mm: 54.5 % of subjects as the most successful positions). Power scores of these positions were 2.01 (1.30 – 2.20) (55 mm), 2.05(1.79 – 2.34) (65 mm) and 2.05 (1.86 – 2.21) (75 mm). Fig. 2 shows an exemplary doppler spectrum indicating an analyzable signal.
Conclusion: The first in-human evaluation of our novel ultrasound-based feedback device yielded promising results showing quick deployment and reliability of measurement in a first cohort of volunteers. The data set the stage for further evaluation in healthy volunteers before testing in patients with critical cardiocirculatory state and under cardiopulmonary resuscitation.